Molds and dies have been hitherto manufactured in the following way: In usual instances, a workplace is first cut using a cutting machine and then machined by electrical discharging in an insulating medium of an electrical discharge machine so that the workpiece is die-sinked, bored or cut by causing continuous spark discharge between the workpiece and a work electrode. In recent years, it has been proposed to directly impart to a cutting machine the function of electrical discharge machining for the purposes of omitting the troublesome operations to set up the change-over from cutting to electrical discharge machining, decreasing the mold and die manufacturing cost, e.g., saving an installation area for a machine, or improving the machining precision.
Incidentally, used as cutting fluids are solutions having good performance in lubricity, rust prevention and non-flammability, which, however, are not suitable for electrical discharge machining because of their low electrical resistivity. On the other hand, used as fluids for electrical discharge machining are those having a high electrical resistivity and good performance in recovering electrical resistivity by ion-exchange treatment (i.e., electrical discharge machining continuity), which, however, can not promise any rust prevention or lubricity and are not suitable for cutting. Accordingly, when the function of electrical discharge machining is imparted to cutting machines, it has been necessary to use a working fluid exclusively used for the cutting when cutting is carried out and to use a working fluid exclusively used for the electrical discharge machining when electrical discharge machining is carried out. Using different fluids in different steps in this way has brought about the problem of a serious lowering of operating efficiency.
An object of the present invention is to solve the above problem and provide a working fluid applicable to both the cutting and the electrical discharge machining.